Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $212.96   11.663%   $237.7975   $237.80   $237.80   $237.80  
  Purchase #2 $225.37   11.613%   $251.5422   $251.54   $251.55   $251.50  
  Purchase #3 $90.37   12.568%   $101.7277   $101.73   $101.75   $101.70  
  Purchase #4 $216.39   13.826%   $246.3081   $246.31   $246.30   $246.30  
  Purchase #5 $133.37   13.464%   $151.3269   $151.33   $151.35   $151.30  
  Purchase #6 $218.40   10.347%   $240.9978   $241.00   $241.00   $241.00  
  Purchase #7 $178.38   11.858%   $199.5323   $199.53   $199.55   $199.50  
  7 purchase totals = $1,275.24       $1,429.2325   $1,429.24   $1,429.30   $1,429.10